1. Field of the Invention
The present invention relates to a mobile antenna apparatus mounted on a mobile body such as an automobile or a ship for receiving radio waves transmitted from an artificial satellite including a broadcast satellite.
A conventional antenna apparatus for a mobile body, as disclosed in JP-A-2-159802, has a flat antenna unit divided into a plurality of antennas. Drive signals of the flat antenna in the elevation and azimuth directions are generated from a phase angle representing a delay phase of a signal received by a second antenna with respect to that received by a first antenna, and motors are driven through motor drivers on the basis of the drive signals to control the antenna attitude, thereby performing automatic tracking to keep the antenna directed toward the satellite.
The conventional receiving antenna apparatuses for receiving satellite broadcast, which detect the direction to the satellite on the basis of phase difference between the received signal of a first antenna and that of a second antenna, have the disadvantage that once a signal delay occurs due to conduit length or wiring length or characteristics of intermediate circuit from the antenna to phase difference detection circuit, the phase difference detection circuit undesirably produces a phase difference output including the above-mentioned signal delay, which lead to erronous direction of the satellite. To obviate this problem, the wiring length is finely adjusted to eliminate the phase difference at the time of assemblage.
This adjustment of wire length is made on trial-and-error basis and consumes a long time.